High NA solid catadioptric focusing device having a flat kinoform phase profile

ABSTRACT

A magneto-optical head using a catadioptric focusing device comprised of an incident surface, a bottom reflective surface, a pedestal, and a body. The incident surface is generally flat and is comprised of a central diffractive, optically transmissive facet and a peripheral facet comprised of a kinoform phase profile. In a data writing or reading mode, an incident optical beam, such as a laser beam impinges upon the central facet, and is diffracted thereby. The incident laser beam can be collimated, convergent or divergent. The laser beam passes through the transparent body, and impinges upon the bottom reflective surface. The laser beam is then reflected by the bottom reflective surface, through the body, unto the kinoform phase profile. The laser beam is reflected and refracted by the peripheral kinoform phase profile as a focused beam, through the body, and is focused as a focal point. The focal point is preferably located at, or in close proximity to a pedestal edge, along a central axis, in very close proximity to the disk. This will allow the focused optical beam to propagate toward, or penetrate the disk through evanescent wave coupling, for enabling the transduction of data to and from the disk.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of the following U.S. provisionalpatent application Ser. No. 60/091,788, filed on Jul. 6, 1998, titled“High NA Solid Catadioptric Focusing device Having a Flat Kinoform PhaseProfile”, assigned to the same assignee as the present application, andincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to optical devices, and itparticularly relates to a high numerical aperture (NA) catadioptricfocusing device having a flat kinoform phase profile, for use in datastorage systems such as optical and magneto-optical (MO) disk drives.

2. Description of Related Art

In a MO storage system, a thin film read/write head includes an opticalassembly for directing and focusing an optical beam, such as a laserbeam, and an electromagnetic coil that generates a magnetic field fordefining the magnetic domains in a spinning data storage medium or disk.The head is secured to a rotary actuator magnet and a voice coilassembly by a suspension and an actuator arm positioned over a surfaceof the disk. In operation, a lift force is generated by the aerodynamicinteraction between the head and the disk. The lift force is opposed byequal and opposite spring forces applied by the suspension such that apredetermined flying height is maintained over a full radial stroke ofthe rotary actuator assembly above the surface of the disk.

A significant concern with the design of the MO head is to increase therecording or areal density of the disk. One attempt to achieve objectivehas been to reduce the spot size of the light beam on the disk. Thediameter of the spot size is generally inversely proportional to thenumerical aperture (NA) of an objective lens forming part of the opticalassembly, and proportional to the wavelength of the optical beam. As aresult, the objective lens is selected to have a large NA. However, theNA in objective lenses can be 1 if the focusing spot were in air, thuslimiting the spot size. Another attempt to reduce the spot size and toincrease the recording areal density has been to use solid immersionlenses (SILs) with near field recording, as exemplified by the followingreferences:

U.S. Pat. No. 5,125,750, titled “Optical Recording System Employing aSolid Immersion Lens”.

U.S. Pat. No. 5,497,359, titled “Optical Disk Data Storage System WithRadiation-Transparent Air-Bearing Slider”.

Yet another attempt at improving the recording head performance proposesthe use of near-field optics, as illustrated by the following reference:

U.S. Pat. No. 5,689,480, titled “Magneto-Optic Recording SystemEmploying Near Field Optics”.

A catadioptric SIL system is described in the following references, andemploys the SIL concept as part of the near-field optics:

Lee, C. W., et al., “Feasibility Study on Near Field Optical MemoryUsing A Catadioptric Optical System”, Optical Data Storage, TechnicalDigest Series, Volume 8, pages 137-139, May 10-13, 1998; and

“Parallel Processing”, 42 Optics and Photonics News, pages 42-45, June1998.

While this catadioptric SIL system can present certain advantages overconventional SILs, it does not appear to capture the entire incident,collimated beam. This represents a waste of valuable energy that couldotherwise increase the evanescent optical field.

Other concerns related to the manufacture of MO heads are the extremedifficulty and high costs associated with the mass production of theseheads, particularly where optical and electromagnetic components areassembled to a slider body, and aligned for optimal performance.

SUMMARY OF THE INVENTION

One aspect of the present invention is to satisfy the long felt, andstill unsatisfied need for a near-field optical or MO disk data storagesystem that uses a catadioptric focusing device or lens with a highnumerical aperture (NA), which does not introduce significant spotaberration on the disk.

Another aspect of the present invention is to provide a focusing devicethat has generally flat surfaces that act as reference surfaces andfacilitate its manufacture and its assembly to the head.

The focusing device includes an incident surface, a bottom reflectivesurface, a focal pedestal, and a body. The incident surface is generallyflat and is comprised of a central diffractive, optically transmissivefacet or surface and a peripheral facet or surface comprised of akinoform phase profile. In a data writing or reading mode, the incidentoptical beam, such as a laser beam impinges upon the central facet, andis diffracted thereby. The incident laser beam can be collimated,convergent or divergent.

The laser beam passes through the transparent body, and impinges uponthe bottom reflective surface. The laser beam is then reflected by thebottom reflective surface, through the body, unto the kinoform phaseprofile. The laser beam is reflected and refracted by the peripheralkinoform phase profile as a focused beam, through the body, and isfocused as a focal point. The focal point is preferably located at, orin close proximity to a pedestal edge, along a central axis, in veryclose proximity to the disk. This will allow the focused optical beam topropagate toward, or penetrate the disk through evanescent wavecoupling, for enabling the transduction of data to and from the disk.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention and the manner of attaining them,will become apparent, and the invention itself will be understood byreference to the following description and the accompanying drawings,wherein:

FIG. 1 is a fragmentary perspective view of a data storage systemutilizing a read/write head according to the invention;

FIG. 2 is a perspective view of a head gimbal assembly comprised of asuspension, and a slider to which the read/write head of FIG. 1 issecured, for use in a head stack assembly;

FIG. 3 is an enlarged, side elevational view of a catadioptric focusingdevice or lens forming part of the read/write head of FIGS. 1 and 2, andmade according to the present invention;

FIG. 4 is an enlarged, side elevational view of another catadioptricfocusing device forming part of the read/write head of FIGS. 1 and 2,and made according to the present invention;

FIG. 5 is a top plan view of the catadioptric focusing devices of FIGS.3 and 4;

FIG. 6 is a bottom plan elevational view of the catadioptric focusingdevices of FIGS. 3 and 4; and

FIG. 7 is an enlarged, side elevational view of yet another catadioptricfocusing device forming part of the read/write head of FIGS. 1 and 2,and made according to the present invention.

Similar numerals in the drawings refer to similar or identical elements.It should be understood that the sizes of the different components inthe figures might not be in exact proportion, and are shown for visualclarity and for the purpose of explanation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a disk drive 10 comprised of a head stack assembly 12and a stack of spaced apart magnetic data storage disks or media 14 thatare rotatable about a common shaft 15. The head stack assembly 12 isrotatable about an actuator axis 16 in the direction of the arrow C. Thehead stack assembly 12 includes a number of actuator arms, only three ofwhich 18A, 18B, 18C are illustrated, which extend into spacings betweenthe disks 14.

The head stack assembly 12 further includes an E-shaped block 19 and amagnetic rotor 20 attached to the block 19 in a position diametricallyopposite to the actuator arms 18A, 18B, 18C. The rotor 20 cooperateswith a stator (not shown) for rotating in an arc about the actuator axis16. Energizing a coil of the rotor 20 with a direct current in onepolarity or the reverse polarity causes the head stack assembly 12,including the actuator arms 18A, 18B, 18C, to rotate about the actuatoraxis 16 in a direction substantially radial to the disks 14.

A head gimbal assembly (HGA) 28 is secured to each of the actuator arms,for instance 18A. With reference to FIG. 2, the HGA 28 is comprised of asuspension 33 and a read/write head 35. The suspension 33 includes aresilient load beam 36 and a flexure 40 to which the head 35 is secured.

The head 35 is formed of a slider (or slider body) 47 secured to thefree end of the load beam 36 by means of the flexure 40, and acatadioptric focusing device or lens 50 retained by the slider 47. Thehead 35 further includes an optical beam delivery means, such as awaveguide or a fiber 48. A stationary or a micro-machined dynamic mirror49 with wires 49W, can be secured to a trailing edge 55 of the slider 47at a 45 degree angle relative to the optical beam emanating from thefiber 48, so as to reflect the optical beam onto the focusing device 50,in order to transduce data to and from a storage medium 14 (FIG. 3).

The slider 47 can be a conventional slider or any other suitable slider.In the present illustration, the slider 47 includes a fiber channel forreceiving the optical fiber 48. Though the fiber channel is illustratedas being centrally located along a generally central axis of the slider47, it should be understood that the location of the fiber channel canbe offset relative to the central axis. In a design where the opticalbeam is delivered through free space, for example when a fiber is notused, the optical beam can be transmitted through the fiber channel or awaveguide formed within the fiber channel.

The details of the focusing device 50 will now be described withreference to FIGS. 3, 5 and 6. The focusing device 50 includes anincident surface 100, a bottom reflective surface 105, a focal pedestal110, and a body 115. The incident surface 100 is generally flat and iscomprised of a central diffractive, optically transmissive surface orcentral facet 130 and a peripheral reflector (or facet) 132 comprised ofa diffractive or kinoform phase profile 133. The body 115 is opticallytransparent, and the incident surface 100 is formed on a first side ofthe body 115. The bottom reflective surface 105 is formed on a secondside of the body 105, such that the first of second sides arepreferably, but not necessarily, oppositely disposed. The pedestal 110is formed on the same side as the reflective surface 105.

In a data writing mode, an incident optical beam, such as a laser beam135 impinges upon the central facet 130, and is diffracted thereby. Theincident laser beam 135 can be collimated, convergent or divergent. Thelaser beam 135 passes through the transparent body 115, and impingesupon the bottom reflective surface 105. The laser beam 135 is thenreflected by the bottom reflective surface 105, through the body 115,onto the peripheral reflector 132. The laser beam 135 is refracted bythe kinoform phase profile 133 as a focused beam 135A, through the body115, and is further focused to a focal point 162 located within or onthe surface of the pedestal 110 at, or in close proximity to an edge orsurface of the pedestal 110 that defines a focal plane 163. In apreferred embodiment, the focal point 162 is located at the central axisP, in very close proximity to the disk 14, such that a localizedevanescent field or light 170 interacts with disk 14, for enabling datato be transduced to and from the disk 14. A coil or coil assembly 64 isformed around the pedestal 110 and secured to the body 115, forgenerating a desired write magnetic field. Wire traces 64T (FIG. 3)connect the coil assembly 64 and contact pads 64A (FIGS. 3, 6).

The focused beam 135A defines an angle of incidence θ with the centralplane P. It should be clear that the angle of incidence θ is greaterthan the angle of incidence θ′ had the optical beam 135 not undergonethe sequence of reflections and diffractions as explained herein.Consequently, the NA of the focusing device 50 exceeds that of aconventional objective lens, as supported by the following equation:

NA=n. sin θ,

where n is the index of refraction of the lens body 115. According tothe present invention, it is now possible to select the lens body 115 ofa material with a high index of refraction n, in order to increase NA.

The peripheral kinoform phase profile 133 is formed of a pattern ofrefractive profiles i.e., 200, 201, 202. While only three refractiveprofiles are illustrated, it should be understood that a greater numberof refractive profiles can be selected. The pattern of refractiveprofiles 200, 201, 202 is coated with a reflective surface 210. Inanother embodiment, the peripheral kinoform phase profile 133 can bemade of an appropriate diffractive grating or an appropriate lensstructure such as a Fresnel lens.

The focal pedestal 110 can be formed integrally with lens body 115, andextends below the bottom reflective surface 105.

With particular reference to FIGS. 5 and 6, the focusing device 50 isgenerally cylindrically shaped with a circular cross-section, and isformed within a substrate 225. The transmissive surface 130 (FIG. 5) isconcentric relative to, and is disposed within the reflective surface210. The central facet 130 can simulate holographic or virtual flat,spherical, conical or other suitable diffractive surfaces 233 (shown indashed lines in FIG. 3), while retaining its generally flatconfiguration. The reflective surface 210 is ring shaped. In analternative design, the kinoform phase profile can simulate anaspherical refractive or diffractive surface 234 (shown in dashed linesin FIG. 3), while retaining its generally flat configuration.

The pedestal 110 can be generally conically shaped (with an edge 111shown in dashed line in FIG. 3), cylindrically shaped (as shown in FIG.4), or it can have a trapezoidal (or another suitable) cross-section,and is co-axially and concentrically disposed relative to the bottomreflective surface 105. In an alternative embodiment, the central facet130 includes an alignment ring 237 (shown in dashed lines in FIG. 5),that assists in the alignment of the optical focusing device 50 duringassembly to the slider body 47.

As explained herein the optical focusing device 50 can be made usingmolding, etching, or other suitable manufacturing techniques. Theflatness of the incident surface 100 helps facilitate wafer processingtechniques to be used to mass assemble a lens wafer in which a pluralityof optical focusing devices 50 are formed, to a slider wafer in which aplurality of sliders 47 are formed.

Using the present focusing device 50, it is possible to reduce the spotsize on the disk 14 to less than 0.3 microns. The focusing device 50 canbe made of any suitable transparent material, including but not limitedto glass, crystal, plastic, or a combination thereof.

FIG. 4 illustrates another catadioptric focusing device 400 according tothe present invention. The focusing device 400 is generally similar infunction and design to the focusing device 50, and has its incidentsurface 100A comprised of a peripheral kinoform phase profile 133A. Theperipheral kinoform phase profile 133A is formed of a reflective surface210 that coats a pattern of concentric binary refractive profiles i.e.,420, 421, 422. The resolution of the refractive profiles 420, 421, 422can vary, for example increased, in order to obtain a more precisecontrol over the diffraction of the laser beam 135A.

FIG. 7 illustrates another focusing device 450 according to the presentinvention. The focusing device 450 is generally similar in function anddesign to the focusing devices 50 and 400, and has its incident surface100B comprised of a peripheral kinoform phase profile 133B. Theperipheral kinoform phase profile 133B is formed of a reflective surface210 that coats a pattern of concentric binary refractive profiles i.e.,200, 201, 202 or 420, 421, 422. Whereas in the focusing devices 50 and400, the incident surfaces 100A, 100B are formed integrally with thelens body 115, the incident surface 100B can be formed of a separateplate 100P which is secured to the lens body 115 along a generally flatsurface 455 (shown in a dashed line).

Another optional distinction between the focusing device 450 of FIG. 7and the focusing devices 50 and 400 of FIGS. 3 and 4, respectively, isthat the focal pedestal 110 can be made of a separate plate that issecured to the lens body 115 along a central, non-reflective surface 463of the bottom of the lens body 115.

Though exemplary dimensions of the focusing device 50 and peripheralreflector 132 are shown for illustration purpose, it should be clearthat other patterns can be selected. It should also be understood thatthe geometry, compositions, and dimensions of the elements describedherein may be modified within the scope of the invention and are notintended to be the exclusive; rather, they can be modified within thescope of the invention. Other modifications can be made whenimplementing the invention for a particular environment. The use of thefocusing device is not limited to data storage devices, as it can beused in various other optical applications, including but not limited tohigh resolution microscopy, surface inspection, and medical imaging.

What is claimed is:
 1. A focusing device comprising: an opticallytransparent body; an incident surface formed on a first side of saidbody; a reflective surface formed on a second side of said body; a focalpedestal formed on said second side; and said incident surface beinggenerally flat and comprised of a central diffractive, opticallytransmissive facet and a peripheral facet comprised of a kinoform phaseprofile.
 2. A focusing device according to claim 1, wherein said firstside and said second sides are oppositely disposed.
 3. A focusing deviceaccording to claim 2, wherein when an incident optical beam impingesupon said central facet, the optical beam is diffracted by said centralfacet, passes through said body, impinges upon said reflective surface,is reflected by said reflective surface through said body onto saidperipheral facet where it is refracted by said kinoform phase profile asa focused beam, through said body, onto a focal point located within oron a surface of said pedestal, such that a localized evanescent field isgenerated.
 4. A focusing device according to claim 3, wherein said focalpoint is located along a central axis and forms an angle of incidence 0therewith.
 5. A focusing device according to claim 4, wherein saidincident optical beam is collimated.
 6. A focusing device according toclaim 4, wherein said incident optical beam is convergent.
 7. A focusingdevice according to claim 4, wherein said incident optical beam isdivergent.
 8. A focusing device according to claim 4, wherein saidincident optical beam is convergent.
 9. A focusing device according toclaim 3, having a numerical aperture NA defined by the followingequation: NA=n. sin θ, where n is the index of refraction of said body.10. A focusing device according to claim 9, wherein said kinoform phaseprofile is formed of a pattern of refractive profiles.
 11. A focusingdevice according to claim 9, wherein said pattern of refractive profilesis coated with a reflective surface.
 12. A focusing device according toclaim 3, wherein said pedestal is formed integrally with said body andextends below said reflective surface.
 13. A focusing device accordingto claim 3, wherein said pedestal is separate from, and is secured tosaid body.
 14. A focusing device according to claim 3, wherein said bodyis generally cylindrically shaped and substantially encapsulated withina protective substrate.
 15. A focusing device according to claim 14,wherein said transmissive facet is concentric relative to, and isdisposed within said peripheral facet.
 16. A focusing device accordingto claim 3, wherein said central facet simulates any of a holographicsurface, a spherical surface, or a conical diffractive surface whileretaining its generally flat configuration.
 17. A focusing deviceaccording to claim 3, wherein said reflective surface is generally ringshaped.
 18. A focusing device according to claim 3, wherein saidkinoform phase profile simulates an aspherical diffractive surface,while retaining its generally flat configuration.
 19. A focusing deviceaccording to claim 3, wherein said pedestal is generally any ofconically or cylindrically shaped.
 20. A focusing device according toclaim 3, wherein said incident surface is formed of a separate platewhich is secured to said body along a generally flat surface. 21.Afocusing device comprising: an optically transparent body; an incidentsurface formed on a first side of said body; a reflective surface formedon a second side of said body; a focal pedestal formed on said secondside; and said incident surface being generally flat and comprised of acentral diffractive, optically transmissive facet and a peripheral facetcomprised of a diffractive-reflective profile.
 22. A focusing deviceaccording to claim 21, wherein said first side and said second sides areoppositely disposed.
 23. A focusing device according to claim 22,wherein a focal point of the focusing device is located along a centralaxis and forms an angle of incidence 0 therewith.
 24. A focusing deviceaccording to claim 23, having a numerical aperture NA defined by thefollowing equation: NA=n. sinθ, where n is the index of refraction ofsaid body.